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author | Vitaly Kuznetsov <vkuznets@redhat.com> | 2017-03-03 14:21:41 +0100 |
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committer | Thomas Gleixner <tglx@linutronix.de> | 2017-03-11 14:47:28 +0100 |
commit | 0733379b512ce36ba0b10942f9597b74f579f063 (patch) | |
tree | 89f45817ac0f3349076798b75a59f62a17cf0d9a /arch/x86/hyperv | |
parent | bd2a9adaadb8defcaf6c284bca7ff41634105f51 (diff) | |
download | linux-stable-0733379b512ce36ba0b10942f9597b74f579f063.tar.gz linux-stable-0733379b512ce36ba0b10942f9597b74f579f063.tar.bz2 linux-stable-0733379b512ce36ba0b10942f9597b74f579f063.zip |
x86/hyperv: Move TSC reading method to asm/mshyperv.h
As a preparation to making Hyper-V TSC page suitable for vDSO move
the TSC page reading logic to asm/mshyperv.h. While on it, do the
following:
- Document the reading algorithm.
- Simplify the code a bit.
- Add explicit READ_ONCE() to not rely on 'volatile'.
- Add explicit barriers to prevent re-ordering (we need to read sequence
strictly before and after)
- Use mul_u64_u64_shr() instead of assembly, gcc generates a single 'mul'
instruction on x86_64 anyway.
[ tglx: Simplified the loop ]
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Dexuan Cui <decui@microsoft.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: devel@linuxdriverproject.org
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: virtualization@lists.linux-foundation.org
Link: http://lkml.kernel.org/r/20170303132142.25595-3-vkuznets@redhat.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'arch/x86/hyperv')
-rw-r--r-- | arch/x86/hyperv/hv_init.c | 36 |
1 files changed, 4 insertions, 32 deletions
diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c index bb1ea58ecd7a..7f5152356a59 100644 --- a/arch/x86/hyperv/hv_init.c +++ b/arch/x86/hyperv/hv_init.c @@ -38,39 +38,11 @@ struct ms_hyperv_tsc_page *hv_get_tsc_page(void) static u64 read_hv_clock_tsc(struct clocksource *arg) { - u64 current_tick; + u64 current_tick = hv_read_tsc_page(tsc_pg); + + if (current_tick == U64_MAX) + rdmsrl(HV_X64_MSR_TIME_REF_COUNT, current_tick); - if (tsc_pg->tsc_sequence != 0) { - /* - * Use the tsc page to compute the value. - */ - - while (1) { - u64 tmp; - u32 sequence = tsc_pg->tsc_sequence; - u64 cur_tsc; - u64 scale = tsc_pg->tsc_scale; - s64 offset = tsc_pg->tsc_offset; - - rdtscll(cur_tsc); - /* current_tick = ((cur_tsc *scale) >> 64) + offset */ - asm("mulq %3" - : "=d" (current_tick), "=a" (tmp) - : "a" (cur_tsc), "r" (scale)); - - current_tick += offset; - if (tsc_pg->tsc_sequence == sequence) - return current_tick; - - if (tsc_pg->tsc_sequence != 0) - continue; - /* - * Fallback using MSR method. - */ - break; - } - } - rdmsrl(HV_X64_MSR_TIME_REF_COUNT, current_tick); return current_tick; } |